1. Technical Field
The present invention relates to a liquid ejecting head and a liquid ejecting apparatus that eject droplets from nozzles in response to displacement of a piezoelectric element as well as an actuator equipped with a piezoelectric element.
2. Related Art
Representatives of liquid ejecting heads include ink jet recording heads, which eject ink droplets from nozzles thereof after the pressure chambers thereof is pressurized by a pressure generator. Examples of the pressure generator for ink jet recording heads include a piezoelectric element obtained by sandwiching a piezoelectric layer made of a piezoelectric material functioning as an electromechanical transducer with two electrodes. This piezoelectric element is deformed to bend, pressurizing the pressure chambers of the head, and thus the nozzles of the head eject ink droplets.
An example of the piezoelectric layer for piezoelectric elements, proposed in JP-A-2007-088446, is a monoclinic layer containing titanium (Ti) and zirconium (Zr) at an elemental ratio (composition ratio) Zr/(Zr+Ti) in the range of 0.5 to 0.8.
Another example of the piezoelectric layer, proposed in JP-A-2005-119166, is one containing Ti and Zr in which the crystal system thereof is tetragonal when the composition ratio Zr/(Zr+Ti) is approximately 0.50.
Incidentally, the crystal system of a piezoelectric layer made of a perovskite-structured material, such as lead zirconate titanate (PZT), usually depends on the composition ratio of Ti and Zr. For example, a bulk PZT piezoelectric layer, to which no external stress is applied and no restrictions are given by a substrate or the like, has a tetragonal crystal system when the composition ratio Ti/(Zr+Ti) is approximately 0.50 or higher, or when the composition ratio Zr/(Zr+Ti) is lower than approximately 0.50; however, it has a rhombohedral or monoclinic crystal system when the composition ratio Ti/(Zr+Ti) is lower than approximately 0.50. In other words, a PZT piezoelectric layer has a composition ratio Ti/(Zr+Ti) of approximately 0.50 in morphotropic phase boundaries (MPBs) between the tetragonal and rhombohedral crystals.
The piezoelectric properties of a piezoelectric layer depends not only on the composition of the layer, but also on the crystal system of the layer. However, as described above, the crystal system of a piezoelectric layer for a piezoelectric element usually changes with the composition of the layer; many literatures including the above-mentioned patent publications have proposed the composition and crystal system of a piezoelectric layer, all stating that the crystal system of the piezoelectric layer depends on the composition of the layer. Furthermore, the composition of a piezoelectric layer is limited by such factors as the relationship between the lattice constant of the piezoelectric layer and that of the base layer and thus cannot be freely adjusted; as a result, piezoelectric layers have limitations on characteristics. This has made it difficult to improve the displacement properties of a piezoelectric element by adjusting the piezoelectric properties of the piezoelectric layer. The recent demand for more improved displacement properties of piezoelectric elements is even more difficult to satisfy.
This problem is not exclusive to piezoelectric elements for ink jet recording heads; those for other liquid ejecting heads and actuators for devices other than liquid ejecting heads have also suffered from the same difficulties.